Self-contained power units, such as electro-hydraulic actuators, are known. A typical electro-hydraulic actuator includes an electric motor that drives a hydraulic pump to move fluid between a reservoir and a hydraulic actuator. The hydraulic actuator generally includes a tubular barrel in which a piston having a piston rod moves linearly, back and forth. The piston seals and separates the inside of the barrel into two chambers, a fluid chamber and a piston chamber. The fluid chamber generally is filled with a substantially incompressible hydraulic fluid, typically an oil.
The pressure of hydraulic fluid pumped into or out of the fluid chambers moves the piston within the barrel. In general, when the electric motor is driven in a first rotational direction, the hydraulic pump moves the fluid into the fluid chamber of the hydraulic actuator and out of the piston chamber, thereby extending a piston rod from the actuator housing. When the electric motor is driven in a second rotational direction, opposite the first rotational direction, the hydraulic pump moves the hydraulic fluid out of the fluid chamber and into the piston chamber, thereby retracting the rod.
Some electro-hydraulic actuators have a hydraulic pump with two intake ports, both located at the bottom of the fluid reservoir. Depending on the end use of the electro-hydraulic actuator and its resulting orientation, one of the intake ports typically is plugged and the other intake port provides a path for fluid flow from the reservoir to the pump. As a result, these electro-hydraulic actuators require a change of components (i.e., the plug) depending upon its orientation at its end use.
An exemplary electro-hydraulic actuator has an external reservoir, thereby allowing it to be used in any orientation without changing components. The reservoir is connected to the pump intake or inlet port through a flexible tube with an affixed weight to ensure that the fluid pick-up end of the tube is always submerged, regardless of orientation. While this design represents a simplistic approach to providing universal orientation, the requirement for an external reservoir adds to the overall space claimed by the electro-hydraulic actuator. Additionally, for electro-hydraulic actuators that change orientations during use, the continuous movement of the flexible tube due to the weight may result in wear or premature failure.